console.log('hello');
let a;
a = 10;
let s;
let e = "str";
//unknown 赋值给别人需要先判断类型
if (typeof e === "string") {
    s = e;
}
//或者类型断言
s = e;
s = e;
function fn(num) {
    if (num > 0) {
        return; //不应有返回值
    }
    else {
        return undefined;
    }
}
function fn2() {
    throw new Error("出错了"); //就是执行不完 一定会出错
}
